Multi-piece intake manifold

ABSTRACT

A multi-piece bi-level engine intake manifold comprises a main body, a top cover member and a bottom cover member. The main body has a pair of upwardly opening channels and a downwardly opening channel in communication with discharge ports, the downwardly opening channel being in communication through an opening in the level portion of the manifold with one of the upwardly opening channels. The upwardly opening channels are closed at their upper surfaces by the top cover member, and the downwardly opening channel is closed at its lower surfaces by the bottom cover member.

11] 3,831,566 Aug. 27, 1974 United States Patent 1191 Thomas MULTI-PIECE INTAKE MANIFOLD Publishing Co., page 131.

[75] Inventor: Thomas G. Thomas, Bedford, Ind. C k et 1 10 1972 D Pub T903020- [73] Assignee: General Motors Corporation,

Detroit, Mich.

ge, Jr.

[22] Filed: May 31, 1973 [21] App]. No.: 365,546

Attorney, Agent or Firm-Paul Fitzpatrick [57] ABSTRACT A multi-piece bi-level engine intake manifold comprises a main body, a top cover member and a bottom cover member/The main b0 [52] US. Cl. 123/52 MV, 123/52 M [51] Int. F02b 29/00 [58] Field of Search 123/52 MV, 52 M, 52 MC,

123/198 E, 188 M, 195 S dy has a pair of upwardly References cued opening channels and a downwardly opening channel UNITED STATES PATENTS in communication with 8/1954 wardly opening chann 2/1971 12/ 1971 l2/ 1973 discharge ports, the downel being in communication g in the level portion of the manithe upwarcll through an openin fold with one of y opening channels. The upwardly opening channels are closed at their upper surfaces by the top cover member, and the downwardly opening channel is closed at its lower surfaces by the bottom cover member.

123 52 MV 123/188 MX 123/ 5 MVX 2,686,506 Carpentier et a1. 3,561,408 Weiand.................... 3,628,512 3,780,715 Elitg ..,1.

FOREIGN PATENTS OR APPLICATIONS 1,286,368 4/1961 France OTHER PUBLICATIONS Basic Carburetion And Fuel Systems No. 2

Petersen 5 Claims, 14 Drawing Figures PAIENTEBMIBZYIBH 3.881.566 MEI if 4 BACKGROUND OF THE INVENTION This invention relates to internal combustion engine intake manifolds and particularly to castable or moldable bi-level intake manifolds.

A V-S internal combustion engine intake manifold is normally interposed between the cylinder banks under the carburetor in such a manner that the discharge ports of the manifold are sealed in communication with the inlet ports of the cylinders, and the inlet openings of the manifold are in communication with the outlet of the carburetor. Moreover, to provide uniform cylinder inlet conditions, the fluid passages provided within the intake manifold are so arranged that two successively firing cylinders will not draw fuel from the same passage. In addition, since the intake manifold passages are desirably arranged so as to provide substantially uniform flow length between the intake manifold inlet openings and discharge ports, some of the manifold passages are so arranged as to cross over other passages, and an intake manifold structure is thus created which has a multi-level passage arrangement not readily adapted to economical and simple casting or mold ing techniques. In particular, the casting or molding of such intake manifolds requires the use of loose disposable coring such as sand coring to form the inner passages.

SUMMARY OF THE INVENTION My invention is an intake manifold capable of being made by simple casting or molding processes in combination with simple assembly methods. The intake manifold comprises three separate members a main body portion, a top cover member and a bottom cover member each of which is castable or moldable in simple two-part dies. The main body portion contains upwardly and downwardly opening passages which, when the main body portion is assembled with the top and bottom cover members, form the required internal passages without the need for loose disposable coring.

The three-piece design of my intake manifold provides additional benefits in assembly and design. In engine assembly situations where the intake manifold involves sophisticated attachments such as those required for fuel injection systems, the top cover member can be assembled with these attachments as a unit without the necessity of handling the entire bulky intake manifold. In addition, the separate portions of the intake manifold can be made from different materials for economy. appearance or other reasons as desired.

Further details and advantages of this invention will be apparent in the following description and drawings.

DESCRIPTION OF THE DRAWINGS FIG. I is an exploded view from the top left front perspective of an intake manifold according to this invention.

FIG. 2 is a perspective view from the bottom left front of the intake manifold of FIG. 1.

FIG. 3 is a section view along line 3-3 in FIG. 1.

FIG. 4 is a section view along line 4-4 in FIG. 1.

FIG. 5 is a section view along line 5-5 in FIG. 1.

FIG. 6 shows a first alternate embodiment of the passage shown in FIG. 4.

FIG. 7 shows a second alternate embodiment of the passage shown in FIG. 4. I

FIG. 8 shows a third alternate embodiment of the passage shown in FIG. 4.

FIG. 9 shows a fourth alternate embodiment of the passage shown in FIG. 4.

FIG. 10 is an exploded view of the intake manifold of this invention modified for exhaust crossover heating.

FIG. 11 is a section view along line 11-11 in FIG. FIG. 12 is a section view along; line 12-12 in FIG. 1 10. 13 is a section view along line 13 13 in FIG. ::FIG. 14 is a section view along line 14-14 in FIG.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to FIG. 1, an intake manifold is shown comprising three elements: a main body 2, a top cover 3, and a bottom cover 4. The main body 2 comprises a base wall 6 extending between a pair of longitudinally extending side walls 8 and 9. The intake manifold is placed on the top of a V-8 engine between the cylinder banks so that side wall 8 is positioned against the inside of the left-hand cylinder bank and side wall 9 is positioned against the inside of the right-hand cylinder bank, the front of the manifold appearing to the left in FIG. 1 and the rear appearing to the right.

The left-hand side wall 8 has formed therethrough, as shown in FIG. 2, four longitudinally spaced discharge ports, numbered from front to rear, 11, 13, 15 and 17; and the right-hand cylinder bank 9 has four similarly spaced discharge ports l2, l4, l6 and 18. When the manifold is mounted on the engine, the discharge ports 11 18 are in communication with. the intake passages of cylinder 1 8, respectively, of the engine.

Most of the base wall 6 forms a level base wall portion 20 which joins side wall 8 in a from location below discharge ports 11 and 13 and a rear location below discharge ports 15 and 17 and joins side wall 9 in a front location below discharge ports 12 and 14 and a rear location below discharge ports 16 and 18. Upper wall means comprising a plurality of substantially vertical walls rise from the top surface of the level base wall portion 20. The upper wall means include a front upper wall 22 which joins side wall 9 immediately in front of discharge port 12 and extends to side wall 8, which it joins between discharge ports 11 and 13, and a rear upper wall 24, which joins side wall 9 on the rear side of discharge port 18 and extends to join side wall 8 between discharge ports 15 and 17. The upper wall means also includes a right upper wall 26, both ends of which join the side wall 9 between discharge ports 14 and 16, a left upper wall 28, both ends of which join the side wall 8'between discharge ports 13 and 15, and an inner upper wall 30, one end of which joins the side wall 9 between discharge ports 12 and 14 and the other end of which joins side wall 9 between discharge ports 16 and 18. It can be readily seen that, when the top cover 3 is attached sealingly to the top surfaces of the upper walls 22, 24, 26, 28 and 30, these parts form two chambers 32 and 34 above the level base wall portion 20. Chamber 32 is in communication with discharge ports 14 and l6; and chamber 34 is in communication with discharge ports l2, l3, l5 and 18.

The base wall 6 also includes a bi-level base wall portion which comprises front and rear bi-level base walls 36 and 37, respectively. The front bi-level base wall 36 rises from the middle front of the level base wall portion to the side wall 8, which it joins above the discharge port 11. The entire rear edge of the front bilevel base wall 36 ajoins the front upper wall 22; and the.end of the front bi-level base wall 36 adjacent the side wall 8 has formed therethrough an opening 40. The opening 40 is necessary for the formation of the discharge port 11 during the manufacture of the main body 2 in a two-part die but is sealingly closed by the top cover 3 when the manifold is assembled. The rear bi-level base wall 37 extends fromthe middle rear of the level base wall portion 20 adjacent the rear upper wall 24 to the side wall 8, which it joins above the discharge port 17. The rear bi-level base wall 37 has an opening 41 formed therein adjacent the side wall 8 and similar to opening 40 in purpose, the opening 41 also being sealingly closed by the top cover 3 in the assembled manifold.

Attached to the underside of the base wall 6 are lower wall means comprising, as seen in FIG. 2, outer and inner lower walls 42 and 44, respectively. The outer lower wall 42 joins the side wall 8 directly in front of the discharge port 11 and extends from there along the front edge of the front bi-level base wall 36. From the end of the latter it turns rearward and continues along the bottom, from front to rear, of the level base wall portion 20, passing under the innermost part of the right upper wall 26. At the rear of the level base wall portion 20, it turns to follow the rear edge of the rear bi-level base wall 37 to join side wall 8 to the rear of the discharge port 17. The inner lower wall 44 has a central portion extending from front to rear along the bottom surface of the level base wall portion 20 on the left side of the outer lower wall 22 and front and rear portions which bend toward the side wall 8, gradually ascend and merge with the front upper wall 22 and the rear upper wall 24, respectively. When the bottom cover 4 is attached sealingly to the outer and inner lower walls 42 and 44 in any one of the number of ways to be described below, it forms, along with the outer and inner walls 42 and 44, the front and rear bi-level base walls 36 and 37 and the level base wall means 20, a chamber 46 in communication with'discharge ports 11 and 17. The level base wall means 20 has an opening 47 therethrough between the right and inner upper walls 26 and 30 and between the outer and inner lower walls 42 and 44, by means of which chamber 32 communicates with chamber 46.

The top cover 3 has a raised inlet portion 48 formed thereon, which inlet portion 48 has a pair of transversely spaced inlet openings 50 and 51 formed therethrough. The inlet openings 50 and 51 are located so that, when the top cover 3 is attached to the main body 2, inlet opening 50 communicates with chamber 34 and inlet opening 51 communicates with chamber 32 and, by means of opening 47, with chamber 46. The top cover 3 is bolted to the main body 2 with a sealing means between them, the sealing means being of the standard type such as gaskets or sealing materials applied to the upper surfaces of the upper wall means of the main body 2.

The bottom cover 4 may be stamped or pressed from sheet metal and attached to the bottom of the main body 2 in a number of ways. FIGS. 3, 4 and 5 show a preferred method of attaching the bottom cover 4 in which the bottom cover 4 fits within recessed portions of the lower walls and the lower ends of the lower walls are peened over to hold the bottom cover 4 in place. FIG. 6 shows an alternate arrangement in which the lower cover 4 is bolted to the bottom of the lower walls. In FIG. 7, the lower walls are provided with downwardly projecting flanges, which can be rolled over to hold the bottom cover 4 in place. Appropriate standard gaskets or sealing materials can be used, if necessary, in any of these arrangements.

FIGS. 8 and 9 show alternative shapes for the members that form the ends of the chamber 46 leading to discharge ports 11 and 17. In FIG. 8 the front bi-level base wall 36 stays at the lower level until it almost reaches the side wall 8, at which point it turns abruptly upward. The side wall 8 is slightly modified and a completely flat bottom cover 4 can be used. Another variation is shown in FIG. 9, in which both the front bi-level base wall 36 and the bottom cover 4 slant upward at a constant slope toward the side wall 8.

In accordance with usual practice, a water coolant passage is provided near the front of the manifold between coolant ports 81 and 82 in side walls 8 and 9, respectively, whereby engine cooling fluid such as water can pass between the engine banks. The coolant crossover passage 80 is formed, as shown in FIG. 1, by a front coolant wall 83, base coolant wall 84 and rear coolant wall 85, all of which extend between side walls 8 and 9 to form a U-shaped trough between coolant ports 81 and 82. Together with the top cover 3, which sealingly engages the top surfaces of front and rear coolant walls83 and 85, this trough defines the crossover passage.

A useful variation of the embodiment described above is an intake manifold with an exhaust heater crossover, as shown in FIGS. 10 14. The exhaust heater crossover is a passage 52 extending transversely across the manifold directly under the level base wall portion 20 as shown in FIG. 11 to form a heat exchanger wherein the heat of the exhaust gases is transferred through the level base wall portion 20 to the incoming combustible mixture within chambers 32 and 34. This exhaust passage 52 extends between an exhaust port 53 between discharge ports 13 and 15 in side wall 8 and another exhaust port 54 between discharge ports 14 and 16 in side wall 9. The passage 52 is formed by front and rear exhaust passage walls 56 and 57, respectively, shown in FIG. 14, which extend from side wall 8 to side wall 9 below the level base wall portion 20 but rise to the top level of the upper wall portion between the right upper wall 26 and side wall 9 and between the left upper wall 28 and side wall 8, as shown in FIG. 10. Transversely aligned portions of the outer and inner walls 42 and 44 between exhaust passage walls56 a 57 are removed to allow communication past the inner and outer walls 42 and 44; and the opening 47 is enlarged so that the front and rear exhaust passage walls 56 and 57, together with an upper exhaust passage wall 58, can extend across chamber 46 without severing communication between chamber 46 and chamber 32. The lower surface of the level base wall portion 20 and the upper exhaust passage wall 58 can be ribbed as shown in FIGS. 12 and 14 to aid in the heat transfer process. The bottom of the exhaust passage 52 is formed by an added transverse center portion '62 of the bottom cover 4 and left and right lower exhaust passage walls 64 and 65, which extend between the front and rear exhaust passage walls 56 and 57 and slope inward and downward from just below exhaust port 53 on side wall 8 and just below exhaust port 54 on side wall 9, respectively, until they meet the transverse center portion 62 of the bottom cover 4. The front and rear exhaust passage walls 56 and 57 define, with left upper wall 28 and side wall 8, an opening 68 and, with right upper wall 26 and side wall 9, an opening 69, the purpose of which openings 68 and 69 is similar to that of openings 40 and 41, but for the formation of exhaust ports 53 and 54. When the manifold is assembled, the openings 68 and 69 are sealingly closed by added wing portions 70 and 71 in the top cover 3. The remainder of the construction of this manifold is the same as that of the previously described manifold without an exhaust heater crossover.

ln operation, both manifolds operate identically except for exhaust heating. A combustible mixture from a carburetor, or air, in a fuel injection system, enters the inlet openings 50 and 51 and proceeds into chambers 32, 46 and 34. As each associated cylinder accomplishes its intake stroke, the gases are drawn through the appropriate discharge port of the manifold. This particular manifold has been designed for an engine that draws through the manifold discharge ports in the following order: ll, l8, l4, l3, l6, l5, l7 and 12. It can thus be seen that, considering chamber 46 as part of chamber 32, the discharge ports draw alternately from chambers 32 and 34. In addition, the lengths of the flow paths within the manifold for all discharge ports are similar.

In the exhaust heater crossover version of the manifold, the air or mixture entering the manifold through inlet openings 50 and 51 flows downward and impinges directly upon the area of the level base wall portion above the exhaust heater crossover passage and is thereby heated.

In addition to the embodiments described, many other embodiments of my invention will occur to those skilled in the art; and, therefore, my invention should be limited solely by the claims which follows.

I claim:

1. A bi-level intake manifold adapted for manufacture without internal coring and for use in a \/-type internal combustion engine having a pair of longitudinally extending, spaced-apart cylinder-heads with intake ports therein, said bi-level intake manifold comprising:

an integrally cast body, top cover means secured to the top of said body in sealing engagement therewith, and bottom cover means secured to the bottom of said body in sealing engagement therewith; said body comprising a pair of side walls extending longitudinally and spaced apart in relation to each other, each of said side walls having a plurality of longitudinally spaced discharge ports therethrough, said side walls adapted to be secured to said cylinder heads with said discharge ports in communication with said intake ports; said body further comprising base wall means extending between and connecting said side walls, said base wall means comprising a level base wall portion having at least one opening therethrough, said level base wall portion being connected to each side wall at a first level thereon below said discharge ports, and at least one bi-level portion connected to said level portion and to a side wall at a second level above said discharge ports; said body further comprising upper wall means rising from said level base wall portion and lower wall means descending from said level and bi-level base wall portions; said top cover means having one or more inlet openings therethrough; said body, top cover means and bottom cover means combining to form one or more chambers, each of said chambers communicating with at least one inlet opening and one discharge port.

2. A bi-level intake manifold adapted for manufacture without internal coring and for use in a V-8 internal combustion engine having a pair of longitudinally extending, spaced-apart cylinder heads with longitudinally spaced intake ports therein, said bi-level intake manifold comprising: an integrally cast body, top cover means secured to the top of said body in sealing engagement therewith, and bottom cover means secured to the bottom of said body in sealing engagement therewith; said body comprising first and second side walls extending longitudinally in spaced-apart relation to each other, each of said side walls having four longitudinally spaced discharge ports therethrough and being adapted for attachment to one of said cylinder heads with said discharge ports in communication with said intake ports; said body further comprising base wall means extending between and connecting said side walls, said base wall means including a level base wall portion and a bi-level base wall portion, said level base wall portion being connected to each side wall at a first level thereon below said discharge ports and having an opening therethrough, said bi-level base wall portion extending laterally from opposite sides of said level base .wall portion between said side walls toward the first said side wall and rising from said first level to connect with said first side wall at a second level above said discharge ports; said body further comprising upper wall means rising from said base wall portion and cooperating with said base wall means, said side walls and said top cover means to form a first chamber in communication with the opening and the middle two discharge ports through the second side wall and a second chamber in communication with the outermost two discharge ports through said second side wall and the middle two discharge ports through said first side wall; said body further comprising lower wall means descending from said base wall portion and cooperating with said base wall means, said first side wall, said bottom cover means and said upper wall means to form a chamber in communication with said opening and the outer two discharge ports through the first side wall; said top cover means having a pair of inlet openings therethrough, one of said inlet openings being in communication with said first chamber and the other of said inlet openings being in communication with said second chamber.

3. The bi-level intake manifold of claim 2 in which each of said side walls has an exhaust port therethrough between the middle two said discharge ports for communication with an exhaust port in one of said cylinder heads; and said upper wall means, lower wall means, base wall means, top cover means and bottom cover means further cooperate to form an exhaust heater crossover passage below said level base wall means to provide communication between said exhaust ports.

4. A bi-level intake manifold adapted for manufacture without internal coring and for use with a V-8 internal combustion engine having a pair of front to rear extending, spaced-apart cylinder heads with longitudinally spaced intake ports therein, said bi-level intake manifold comprising:

an integrally cast body, top cover means secured to the top of said body in sealing engagement therewith, and bottom cover means secured to the bottom of said body in sealing engagement therewith; said body comprising first and second side walls extending front to rear in relation to said engine in spaced-apart relation to each other, said first side wall having, from front to rear, first, third, fifth and seventh longitudinally spaced discharge ports therethrough and said second side wall having, from front to rear, second, fourth, sixth and eighth longitudinally spaced discharge ports therethrough, said side walls being adapted for attachment to said cylinder heads with said discharge ports in communication with said intake ports; said body further comprising base wall means extending between and connecting said side walls, said base wall means including a level base wall portion having an opening therethrough and first and second bi-level base wall portions, said level base wall portion being connected to each of said side walls at a first level thereon below said discharge ports, said first bi-level base wall portion extending from the front of said level base wall portion and rising from said first level to connect with said first side wall at a second level above said first discharge port, said second bi-level base wall portion extending from the rear of said level base wall portion and rising from said first level to connect with said first side wall at said second level above said seventh discharge port; said body further comprising upper wall means rising from said base wall portion, said upper wall means comprising a front upper wall joining said first side wall between said first and third discharge ports and said second side wall in front of said second discharge port, a rear upper wall joining said first side wall between said fifth and seventh discharge ports and said second side wall to the rear of said eighth discharge port, a left upper'wall to the left of said opening, both ends of which join said first side wall between said third and fifth discharge ports, a right upper wall to the right of said opening, both ends of which join said second side wall between said fourth and sixth discharge ports, and a middle upper wall between said left and right upper walls to the left of said opening with one end joining said second side wall between said second and fourth discharge ports and another end joining said second side wall between said sixth and eighth discharge ports; said body further comprising lower wall means descending from said level base wall portion and said bi-level base wall portions, said lower wall means comprising an outer lower wall having one end joining said first side wall in front of said first discharge port and another end joining said first side wall to the rear of said seventh discharge port and passing to the right of said opening and an inner lower wall having ends which merge with the front and rear upper walls near said first side wall and passing to the left of said opening; said level base wall portion, upper wall means and top cover means together forming a first chamber in communication with said second, third, fifth and eighth discharge ports and a second chamber in communication with said fourth and sixth discharge ports; said base wall means, and lower cover means together forming a third chamber in communication with said first and seventh discharge ports and said first chamber; said top cover means having a pair of inlet openings therethrough, one of said inlet openings being in communication with said first chamber and the other of said inlet openings being in communication with said second chamber.

5. The bi-level intake manifold of claim 4 in which the first side wall has an exhaust port therethrough between said third and fifth discharge ports for communication with an exhaust port in one of said cylinder heads; said second side wall has an exhaust port therethrough between said fourth and sixth discharge ports for communication with an exhaust port in the other of said cylinder heads; and said upper wall means, lower wall means, top cover means and bottom cover means cooperate to form an exhaust heater crossover passage below said level base wall means to provide communication between said exhaust ports. l 

1. A bi-level intake manifold adapted for manufacture without internal coring and for use in a V-type internal combustion engine having a pair of longitudinally extending, spaced-apart cylinder heads with intake ports therein, said bi-level intake manifold comprising: an integrally cast body, top cover means secured to the top of said body in sealing engagement therewith, and bottom cover means secured to the bottom of said body in sealing engagement therewith; said body comprising a pair of side walls extending longitudinally and spaced apart in relation to each other, each of said side walls having a plurality of longitudinally spaced discharge ports therethrough, said side walls adapted to be secured to said cylinder heads with said discharge ports in communication with said intake ports; said body further comprising base wall means extending between and connecting said side walls, said base wall means comprising a level base wall portion having at least one opening therethrough, said level base wall portion being connected to each side wall at a first level thereon below said discharge ports, and at least one bi-level portion connected to said level portion and to a side wall at a second level above said discharge ports; said body further comprising upper wall means rising from said level base wall portion and lower wall means descending from said level and bi-level base wall portions; said top cover means having one or more inlet openings therethrough; said body, top cover means and bottom cover means combining to form one or more chambers, each of said chambers communicating with at least one inlet opening and one discharge port.
 2. A bi-level intake manifold adapted for manufacture without internal coring and for use in a V-8 internal combustion engine having a pair of longitudinally extending, spaced-apart cylinder heads with longitudinally spaced intake ports therein, said bi-level intake manifold comprising: an integrally cast body, top cover means secured to the top of said body in sealing engagement therewith, and bottom cover means secured to the bottom of said body in sealing engagement therewith; said body comprising first and second side walls extending longitudinally in spaced-apart relation to each other, each of said side walls having four longitudinally spaced discharge ports therethrough and being adapted for attachment to one of said cylinder heads with said discharge ports in communication with said intake ports; said body further comprising base wall means extending between and connecting said side walls, said base wall means including a level base wall portion and a bi-level base wall portion, said level base wall portion being connected to each side wall at a first level thereon below said discharge ports and having an opening therethrough, said bi-level base wall portion extending laterally from opposite sides of said level base wall portion between said side walls toward the first said side wall and rising from said first level to connect with said first side wall at a second level above said discharge ports; said body further comprising upper wall means rising from said base wall portion anD cooperating with said base wall means, said side walls and said top cover means to form a first chamber in communication with the opening and the middle two discharge ports through the second side wall and a second chamber in communication with the outermost two discharge ports through said second side wall and the middle two discharge ports through said first side wall; said body further comprising lower wall means descending from said base wall portion and cooperating with said base wall means, said first side wall, said bottom cover means and said upper wall means to form a chamber in communication with said opening and the outer two discharge ports through the first side wall; said top cover means having a pair of inlet openings therethrough, one of said inlet openings being in communication with said first chamber and the other of said inlet openings being in communication with said second chamber.
 3. The bi-level intake manifold of claim 2 in which each of said side walls has an exhaust port therethrough between the middle two said discharge ports for communication with an exhaust port in one of said cylinder heads; and said upper wall means, lower wall means, base wall means, top cover means and bottom cover means further cooperate to form an exhaust heater crossover passage below said level base wall means to provide communication between said exhaust ports.
 4. A bi-level intake manifold adapted for manufacture without internal coring and for use with a V-8 internal combustion engine having a pair of front to rear extending, spaced-apart cylinder heads with longitudinally spaced intake ports therein, said bi-level intake manifold comprising: an integrally cast body, top cover means secured to the top of said body in sealing engagement therewith, and bottom cover means secured to the bottom of said body in sealing engagement therewith; said body comprising first and second side walls extending front to rear in relation to said engine in spaced-apart relation to each other, said first side wall having, from front to rear, first, third, fifth and seventh longitudinally spaced discharge ports therethrough and said second side wall having, from front to rear, second, fourth, sixth and eighth longitudinally spaced discharge ports therethrough, said side walls being adapted for attachment to said cylinder heads with said discharge ports in communication with said intake ports; said body further comprising base wall means extending between and connecting said side walls, said base wall means including a level base wall portion having an opening therethrough and first and second bi-level base wall portions, said level base wall portion being connected to each of said side walls at a first level thereon below said discharge ports, said first bi-level base wall portion extending from the front of said level base wall portion and rising from said first level to connect with said first side wall at a second level above said first discharge port, said second bi-level base wall portion extending from the rear of said level base wall portion and rising from said first level to connect with said first side wall at said second level above said seventh discharge port; said body further comprising upper wall means rising from said base wall portion, said upper wall means comprising a front upper wall joining said first side wall between said first and third discharge ports and said second side wall in front of said second discharge port, a rear upper wall joining said first side wall between said fifth and seventh discharge ports and said second side wall to the rear of said eighth discharge port, a left upper wall to the left of said opening, both ends of which join said first side wall between said third and fifth discharge ports, a right upper wall to the right of said opening, both ends of which join said second side wall between said fourth and sixth discharge ports, and a middle upper wall between said left and right upper walls to the left of said opening witH one end joining said second side wall between said second and fourth discharge ports and another end joining said second side wall between said sixth and eighth discharge ports; said body further comprising lower wall means descending from said level base wall portion and said bi-level base wall portions, said lower wall means comprising an outer lower wall having one end joining said first side wall in front of said first discharge port and another end joining said first side wall to the rear of said seventh discharge port and passing to the right of said opening and an inner lower wall having ends which merge with the front and rear upper walls near said first side wall and passing to the left of said opening; said level base wall portion, upper wall means and top cover means together forming a first chamber in communication with said second, third, fifth and eighth discharge ports and a second chamber in communication with said fourth and sixth discharge ports; said base wall means, and lower cover means together forming a third chamber in communication with said first and seventh discharge ports and said first chamber; said top cover means having a pair of inlet openings therethrough, one of said inlet openings being in communication with said first chamber and the other of said inlet openings being in communication with said second chamber.
 5. The bi-level intake manifold of claim 4 in which the first side wall has an exhaust port therethrough between said third and fifth discharge ports for communication with an exhaust port in one of said cylinder heads; said second side wall has an exhaust port therethrough between said fourth and sixth discharge ports for communication with an exhaust port in the other of said cylinder heads; and said upper wall means, lower wall means, top cover means and bottom cover means cooperate to form an exhaust heater crossover passage below said level base wall means to provide communication between said exhaust ports. 